Short fibrillar cellulose ester material (termed fibrets) are employed in a variety of applications such as in the manufacture of tobacco smoke filters and as a replacement for clay and titanium dioxide in paper opacification. Fibrets can be produced using an unstable wet spinning process in which the fibrets are precipitated out of an organic solution of the polymer and formed, in a non-solvent, under controlled conditions. The formed fibrets are in a mixture of the organic solvent and non-solvent. The mixture can then be screened or filtered to increase the fibret concentration and the fibret concentrate thereafter heated to evaporate the organic solvent.
Conventionally, the heating step is conducted indirectly in a steam-jacketed vessel. This method of separating the organic solvent is unsatisfactory because of the formation of large clots of fused fibrets, referred to as "chips", on the heated vessel walls. These chips plug up piping and equipment.
The formation of chips can be eliminated by replacing the indirect heating step with the introduction of live superheated steam into the mixture. The resultant fibrets are chip-free but contain agglomerations of fused fibrets having diameters of less than 1 mm, referred to as "pills".